Signal lantern



Aug. 30, 1932. J c STlMsQN 1,874,138

S IGNAL LANTERN Filed Dec. 10, 1923 I-NVE NTOR. JONATHAN c. STIMSON.

HIS ATTORNEY Patented Aug. 30, 1932 PATENT 4 OFFICE JONATHAN C. STmSON, OF ST. LOUIS, MISSOURI SIGNAL LANTERN Application filed. December 10, 1923. Serial No. 679,724.

This invention relates to light signals and more particularly to signal lanterns and cover glasses therefor.

Traflic movement at night is universally 5 dependent for its safety upon the display of signal lights used either to indicate the location of vehicles themselves, which comprise the traflic, or to give interpretive indications for the control of the traflic movement.

Signal lanterns are the specific agent employed for furnishing the light indication. In spite of the greatest care in the design of lantern equipment and its maintenance, failures frequently 'occur, even when the 5 signalling system is highly developed as in railroad service.

In the case of highway traffic the lantern signals required for safety are largely con fined to proper lights marking the location of automobiles. Automobiles are generally equipped with electric signal lanterns which are eflicient for the purpose, but failures are numerous. Bulbs frequently burn out and electrical connections become faulty. Re-

pairs are easily made, but because of widespread individual ownership and operation it is impossible to enforce the prompt attention which the failure warrants. The menace to safety resulting is not inconsiderable. Also the failure may occur when the automobile is in use and the driver is unaware of the failure. This is especially true of the rear marker which is usually required by law to light toward the point of observation, and

which may impart color to the signal light source. This cover may also. 'be in the form of a condensing lens for the purpose of co1-- lecting the rays from the source in the form of an intensified beam projected in the direction from which it is to be observed. In highway traflic signals employing a lamp a con-' densed signal beam is not necessary as an ordinary light is ordinarily seen at a suflicient distance for safety. In other service employing a lamp signal a condensed beam is not always necessary.

Vehicles attaining any considerable speed at night are almost universally equipped with powerful electric headlights. Reflecting signals have been devised (particularly by the applicant, see Patent No. 1,671,086, May 22, 1928) making use of this headlight source of light and reflecting it back to the driver of the vehicle (if desired in a signal color), thus signalling the location of objects or traflic conditions more positively than the driver could see the object or condition from the direct illumination from his headlight.

Such signals may be used as a duplicate sig-' nal arranged along side of a signal lantern to act in case of the signal lantern failure. Such use, however, is objectionable from two standpoints. First, the reflecting signal is operative whether the signal lantern is burning or not. If the lantern signal is burning then two indications of the same color are given, which is known in the signalling art as double aspect, and may be the code indication for. an entirely different traflic con.- dition than the display of a single signal in the particular color. Second, the duplication of equipment, i. e., a signal lantern and a reflecting signal-is expensive, and for some uses the additional cost may make the double use prohibitive. The use of reflecting signals to the exclusion of signal lanterns is obviously not justified from thestand-point of safety, and is contrary to many existing laws.

One ofthe objects of this invention, therefore, is to provide a signal lantern which will not only show the signal by transmission from the light source of the lantern, but which will also create a signal by reflection of light thereon from a source external to the lantern and which signal will be visible at considerable distances to an observer located a substantial distance outside of a line connecting the reflecting signal lantern with the light source.

Another object of this invention is to provide a cover orglass for signal lanterns, which will accomplish the above object, which is transparent and permits the'transmission of light from the lantern light toward the intended observer, and is so formed that at the same time that it reflects light external to the lantern and impinging upon its front face from varying angles'of' incidence back toward its source, it directs a concentrated spreading beam back towards and visible to an observer located a substantial distance outside of a line connecting the reflecting signal lantern with the light source.

Another object of this invention is to provide a signal lantern with a live signal area and a reflecting signal area which are coincident and which will accomplish the above objects. The term live signal area is used as conveniently descriptive of the lighted window of a signal lantern which has a self contained source of light.

Other objects will appear in the detail description taken in connection with the accompanying drawing, in which:

Figure l is a section through a signal lantern showing one embodiment .of this invention and showing also the optical diagram;

Figure 2 is a face,view of the cover or glass;

Figure 3 is a section on line 33, Figure 2;

Figure 4 is a face view of a cover or glass showing another embodiment of this invention;

Figure 5 is a section on line 55, Figure 4;

Figure 6 is an optical diagram; and

Figures 7 and 8 and Figures 9 and 10 are views similar to Figures 4 and 5, but illus trating other embodiments of this invention;

Generally stated, the signal lantern embodying this invention comprises a casing, a lamp (such as a bulb) therein, and a reflector associated with the lamp and adapted to permit light from the lamp to issue from the casing; this reflector is adapted to reflect light incident thereon from a distant source (as from the headlight of an automobile) back in the general direction of the light source.

It is not, however, sufiicient that the light be reflected back when the impinging beam is exactly normal to the surface of the reflector; for an automobile travels in anything but a straight path and, it is, therefore, rare that one automobile following (or approaching) another will be able to project a beam at right angles to a reflector on the automobile in front. In accordance with this invention,

therefore, the reflector is so constructed that while permitting free transmission of light from the lamp bulb, it will serve to reflect light incident from a distant source back toward the source irrespective (for practical purposes) of the angle of incidence.

Again it is not sufiicient that the light be simply reflected back, but due reference must be had to the intensity of the reflected light.

It is well known that the intensity of a beam varies inversely as the square of the distance, and Where light is cast back by reflection, this path is double that of the distance between the reflector and the light source. Furthermore the intensity of a beam from a given light source, whether emanated by the initial light source or by reflection, varies inversely as the square of the solid angle of the beam cast back. In accordance with this invention, therefore, the reflector is constructed so that while permitting free transmission of light therethrough from the lamp bulb, it operates to slightly spread the reflected light with substantial uniformity throughoutits field of spread in order to direct a slightly spreading and concentrated beam back towards its observer, who may be the driver of the following vehicle.

It is not, however, sufficient that the light be reflected back in simply a straight line to the distant light source, but it must be so reflected as to encompass, say, the driver of the following vehicle, whose eyes are located some distance above and laterally of the automobile headlights. In accordance with this invention, therefore, while the reflector is constructed to freely transmit light from the lamp bulb and while serving to reflect the light incident thereon in the form of a spreading beam, this spread is sufficient to be visible to an observer located a substantial distance outside of the line connecting the reflector with the light sourcein the case of a tail lamp, to encompass the drivers eye on the following automobile.

In accordance with this invention, therefore, the reflector associated with the lamp and adapted to permit light from the lamp to issue from the casing, is positioned and operates to reflect external light incident thereon at varying angles from a distant source, back in the general direction of the alight source, and this reflector has means adapted to slightly spread the reflected light with substantial uniformity throughout its field of spread in order to direct a spreading beam back towards and visible to an observer located a substantial distance outside of a line connecting the reflector with the light source.

In the illustrated embodiment of this invention, the casing has a transparent cover glass which forms the reflecting, as well as the light-transmitting, medium. This glass, in order to function as described, may have hereinafter described, may be 0 the char-- actor in which a series of reflecting surfaces is arranged relatively at approximate right angles and in a circuit about the reflector axis, as described'in Patent No 1,671,086.

Referring to the accompanying .drawing, and more particularly to Figure 1, 2 designates the casing of a signal lantern, which as shown is provided with a light 3 and a cover or glass 4 held in place by a ring 40 in the usual manner. As shown the signal lantern is a so-called tail light of an automobile; it is to be understood, however, that this is for the purpose of illustrating a practical application of this invention, since it is applicable to signal lanterns generally.

The cover or glass 4 is arranged in the lantern aperture in front of the light and is constructed and arranged to not only permit the light to'pass therethrough but also to reflect external light back towards its source in the manner described. For this purpose and in accordance with the embodiment illustrated, the glass has total reflecting prisms or units on the back thereof and arranged in contigpous relation.

As shown in igures 1, 2 and 3.the cover or glass is a transparent prismatic glass plate with one smooth face as indicated in Figure 3. The figured face of the plate is in the form of a series of triple reflector units, 1, arranged in contiguous relation integral with the plate and approximately covering the area of the plate. A triple reflector has three reflecting surfaces intersecting at a common point, and where these surfaces are at a mutual angular relation to each other of 90 degrees has the peculiar property of reflecting light back to its source regardless of the angle of incidence. In the reflector unit described, employed to secure the objects of this invention, the reflecting surfaces are arranged relatively at approximate right angles and in a circuit around the reflector axis, as described in Patent No. 1,671,086. Where the reflectors are made of pressed glass so as to form surfaces, the reflected beam is spread in the form of a cone, in the manner described in the patent and in Patent No. 1,591,572, July 6, 1926, so as to slightly spread the reflected light with substantial uniformity throughout its field of spread in order to direct a concentrated spreading beam back towards and visible to an observer located a substantial distance outside of a line connecting the reflector with the light source.

The patents describe the manner of and the conditions under which the desired results are secured, particularly when the reflector is made of pressed glass. The right angular relationship of the reflecting surfaces is generally maintained, but the surfaces are not optically accurate in the accepted sense of the term, but are purposely only an approximation thereof; it is essential that the surfaces be so formed. in order to carry out the purpose of this invention. The mold or matrix of the reflector is, therefore, constructed with the anglescapproximately accurate, that is, within about one degree of ninety degrees (90), but not within a second or less as is required in an op-' tical device if a defined undistorted image is to be secured. The surfaces of the mold are made as plane as is conveniently possible and are given a degree of polish. If not polished too highly, there are minute irregularities in the surfaces that result in a symmetrical spreading of the light as it is successively reflected upon the three surfaces; the irregularities forming a large number of minute reflecting surfaces of different an-' gles, these surfaces varying sufliciently from a true plane to co-operate-together in the multiple reflection of the three surfaces so as to spread the light to a degree, but not varying sufficiently from ninety degrees (90) to scatter the light out of a defined beam or field. Where the greatest feasible distance visibility is required and the observer is located at a point fairly close to the line connecting the reflector with the source of light, then it is necessary to make the mold for the pressed glass reflector care fully, with a sufficiently high degree of accuracy and polish upon the surfaces so that the reflected beam will be confined to a cone with a small angular spreadjWhen the triple reflectors are prismatic, as shown, the reflecting surfaces do not require the application of an opaque metallic reflecting film to secure reflection, but act according to the well known optical law of total reflection in which the plane of separation between the glass of the reflector and the air is the re fleeting agent. It is the property of reflection from varying angles back toward the source without employing opaque surfaces, as well as the production of a concentrated spreading beam, which is the particular quality of the illustrated reflector advantageously made use of in this invention.

Since it is the object of this invention to provide areflecting signal which is operative at all times as a reflecting signal while co-active as a live-light signal (the area from which the two are'given being co-incident) it is desirable to trace the two types oflight rays which become observable. The path of a light ray originating from a point external to the lantern is shown by a broken line and arrpws. This ray impinges .upon

the reflector 4 normal thereto, is multiply reflected by one of the reflecting units and returned towards its source as shown, since it is the property of a triple reflector to turn back light toward the source regardless of the angle of incidence, within limits. Similarly another ray 102 originating from a point external to the lantern, but in this case from an angle to the normal of the lens-reflector, impinges upon the front face of the lens-reflector and is similarly reflected by one of the prismatic units and returned toward its source. The lantern, therefore, fulfills the purpose of an always active reflecting signal. The lantern is provided with the light source 3, shown as an incandescent bulb, but which may be any desired source of light.

Let us now consider the light source as a point, although the filament of even a small electric lamp really presents a luminous area.

Referring to Figure 1, light originating from this source is radiated in all directions, and since the glass is transparent that portion of the light impinging upon it is transmitted by it, and passes into the area in front of the signal lamp. Because of the permutation of the surfaces forming the rear face of'the glass, theoretically this light is variously refracted and scattered in many directions, not all, of which is visible to observers of the signal located in the usual zone of observance, because of the wide lateral divergence of a part of this light with respect to the axis of the lantern which lies along the path of ray 101. Some of the light, however, is not refracted, or if refracted, it is not deflected greatly from its original general direction. Ray 101, shown as originating from the source 3 by the unbroken line and arrows, is such a ray. It impinges upon the rear face of the cover or glass at a point where two of the units merge into the body part of the plate, and normal thereto, and is, therefore, incident at a point where it is not refracted. Ray 103 is similarly incident at a point where two units join, is not refracted at the rear face of the glass, but is deflected by refraction when passing into the air at the front face, although the direction of its path is not changed sufliciently to make it ineffective to observers of the signal located in the usual zone of observance. Ray 105 has its path deflected similarly to 103 but in this case has its point of incidence at the apex of one of the prismatic units. In the same way all light rays from the source 3 impinging upon the ridges, points and lines of junc ture of the units are not deflected sufliciently to prevent their being effective to observers located within the usual range or zone of observance of the lantern signal such as is used.

for, say, the rear of automobiles. Theoretically the amount of light impinging on the lines and points and transmitted in the proper direction would be negligible; i. e., if the junctures of the surfaces were perfect lines or points, but as the glass is constructed of pressed glass, these junctures are somewhat rounding and allow suflicient transmission of light in the desired direction to make the signal lantern intense enough for ordinary use. Reference to Figure 2 shows that these zones for free transmission exist along all lines shown in the drawing within the hexagonal or prismatic portion of the plate. If the inner walls of the casing 2 are painted with white'or aluminum paint then the light from the source 2 is diffusely reflected by the walls and is transmitted through the glass in many different directions so as to reinforce the intensity of the signal light. This is indicated by rays 107, 107a and 1076.

109 and 111 illustrate rays which impinge upon the prismatic surfaces in such manner as to be sharply refracted laterally. Ray 109 impinges upon a surface perpendicular to the plane of the paper and is refracted as shown. Ray 111, which impinges upon a surface whose plane is at an angle with the plane of the paper, is deflected at an angle not easily shown and is indicated by the dotted lines.

It is to be understood that no attempt is made to show the paths of all typical rays, it simply being indicated that a suflicient amount of light radiated by the source 3 passes through the lens-reflector 4 to create a visible signal of sufiicient intensity for many uses. The cover 4 may be made of colored glass so that both the radiated light and the reflected light is secured in any de-' sired signal color.

In practice a cover glass, as shown in Figures 1, 2 and 3 is, and has been, found entirely suitable for practical employment. Of course, the usual expedient of employing a window may be resorted to by the omission of units at any desired point; however, such an expedient has disadvantages in that it leaves a substantial area which does not func tion as a reflector. A practical way of securing more free transmission, and which does not have the disadvantages, will be described.

The signal lantern of Figures 1, 2 and 3, and its cover or glass illustrates the principle of the invention in its simplest embodiment. Figures 4 to 13, following, show various embodiments of the prismatic structure of the cover or glass for various types of use, and are in no sense to be considered a catalogue of the various forms in which the same may be made in order to carry out the purpose of this invention.

In Figures 4, 5 and 6 the reflecting units or prisms on the back of the cover or glass are interrupted to form freer light transmitting zones. As shown the glass is provided with the zones 5 inserted at the points of juncture of groups of six units, each zone being in the form of a six sided bead or facet having a flat surface parallel to the front face of the lensrtflector. These facets, while affecting the symmetry of the reflecting umts 5 as shown in the cross section, do not affect the reflecting efiiciency of the triple reflectors, so long as the light to be reflected is not at great angular incidence, since these portions of the plate are ineffective for reflecting purposes at relatively small angles. By providmg the facets with faces parallel to the front face, these particular zones in the'cover glass transmit light from the source 3 in the same manner as an unfigured cover glass or window,and reinforce the intensity of the signal beam if that is necessary or desirable. The numbered rays of Figure 6 correspond with the rays of Figure 1, except forthe changesdue to the facets.

In Figures 7 and 8 the triple reflectors have hexagonal apertures so as to form a continuously active area or face which will appear uniformly illuminated. In this case, since all of the area is eflective for reflection, if it is desired to provide zones similar to 5, Figures 4, 5 and 6, for a corresponding purpose, the apices of the reflecting units may be trun cated, as shown in Figures 9 and 10, in which case the reflecting efliciency of the lens-reflector is reduced in the ratio that the area of the plane facets formed by truncation bear'to the entire reflecting area. 7

The feature of interrupting the continuity of the reflector units to provide freer lighttransmitting zones, each of substantial area between the units, is not claimed herein but is claimed in divisional application Serial N 0. 479814, filed September 5,1930.

It is not essential that the transparent prismatic plate forming the cover or glass be constructed with triple reflectors, a though this type of reflector'is more eificient for most purposes.

It is further obvious that various changes may be made in details of construction within the scope of the appended claims, without departing'from the spirit of this invention; it is, therefore, to be understood that this invention is not to be limited to the specific details shown and described.

Having thus described the invention, what is claimed is:

1'. A signal lantern comprising, a casing, a lamp therein, and a reflector associated with said lamp and adapted to permit light from said lamp to issue from said casing, said reflector being positioned and operating to reflect external light incident thereon at varying angles from a distant source back in the general direction of the light source and said reflector having means adapted to slightly spread the reflected light with substantial uniformity throughout its field of spread in order to direct a spreading beam back to- 65 wards and visible to an observer located a permit lig substantial distance outside of a; lineconnect- 1 ing the reflector with the lightsource. a.

2. A signal lantern compris ng, aacasing, a lamp therein, and a transparent reflector on said casin in front of said lamp adapted to %1t from said lamp to issue from said casing through said reflector, said reflector having means adapted to reflect external light incident thereon at varying angles from a distant source back in the general direction of the light source and said reflector having means adapted -to--slightly spread the reflected light with substantial uniformity throughout its field of spread in order to direct a spreading beam back towards and visible to an observer located a substantial distance outside of a line connecting the reflector with the light source.

3. A signal lantern comprising, a casing, a lamp therein, and a transparent reflector on said casing in front of said lamp, said re-' flector having totally reflecting surfaces disposed to permit light from said lamp to issue from said casing, said reflecting surfaces being adapted to reflect external light incident thereon at varying angles from a distant source back in the general direction of the light source and said reflector having means adapted to slightly spread the reflected light with substantial uniformity throughout its field of spread in order to direct a spreading beam back towards and visible to an observer located a substantial distance outside of a line connecting the reflector with the light source. 4. A signal lantern comprising, a casing, a lamp therein, and a transparent reflector on said casing in front of said lamp, said reflector having totally reflecting surfaces on the back thereof and in front of said lamp disposed to permit light from said lam to issue freely through said reflector and rom said casing, said reflecting surfaces being constructed and arranged to reflect external light incident thereon at varying angles from a distant source back in the general direction of the light source and said reflector having means adapted to slightly spread thereflected light with substantial uniformity throughout its field of spread in order to direct a spreading beam back towards and visible to an observer located a substantial 1 distance outside of a line connecting the .re-

flector with the light source.

5. A signal lantern comprising, a casing, a lamp therein, and a transparent reflector on said casing in front of said lamp, said reflector having totally reflecting units on the back thereof and in front of said lamp to permit light from said lamp to issue freely from said casing, each of said units having a series of reflecting surfaces arranged relatively at approximate right angles and in a circuit around the axis thereof in order to reflect external light incident thereon at varying angles from 'a distant source back in the general direction of the light source and said reflector having means adapted to slightly spread the light reflected by the surfaces of the several units with substantial uniformity 5 throughout their fields of spread in order to direct spreading beams back towards and visible to an observer located a substantial distance outside of a line connecting the reflector with the li ht source.

In testimony w ereof I aifix my signature this 8th day of December, 1923.

' JONATHAN C. STIMSON.

BEST AVAILABLE COPY CERTIFICATE OF CORRECTION.

Patent No. 1,874,138. August 30, 1932.

JONATHAN C. STIMSON.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, line 122, after "signal" insert the 'word "lantern"; page 5. line [06, claim 4, strike out the words "freely through said reflector and"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office. 7

Signed and sealed this 7th day of February. A. D. 1933.

M. J. Moore.

(Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 1,874,138. August 30, I932.

JONATHAN C. STIMSON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, line l22. after "signal" insert the 'word "lantern"; page 5. line 106, claim 4, strike out the words "freely through said reflector and"; and that the said Letters Patent should he read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of February. A. D. 1933.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

